1. Field of the Invention
The present invention relates to a surface light source control apparatus and a surface light source control method for a direct exposure apparatus which, using a surface light source constructed from a plurality of point light sources, projects light onto an exposure surface of an exposure target (exposure target substrate) moving relative to the surface light source.
2. Description of the Related Art
Generally, a wiring pattern on a wiring substrate is formed by exposing the substrate based on wiring pattern design data and by developing the desired pattern on the substrate, followed by etching. In one method of exposure, the exposure is performed using a photomask.
On the other hand, a patterning method based on direct exposure that does not use photomasks has been proposed in recent years. According to this method, since corrections for the expansion, shrinkage, distortion, misalignment, etc. of the exposure target (exposure target substrate) can be made in real time or in advance at the exposure data generation stage, remarkable improvements can be achieved in such aspects as an improvement of the manufacturing accuracy, an improvement of the manufacturing yield, a reduction of the delivery time, and a reduction of the manufacturing cost.
As one example of the patterning method based on direct exposure, Japanese Unexamined Patent Publication No. 10-112579 discloses a method that forms an exposure pattern by direct exposure using a Digital Micromirror Device (DMD).
FIG. 7 is a diagram illustrating one prior art example of a direct exposure apparatus using the DMD. When directly exposing the resist formed on an exposure target substrate 3 moving relative to the DMD 51, pattern data corresponding to the pattern to be exposed is generated by a pattern generator 52, and this pattern data is applied to the DMD 51. The pattern generator 52 operates in conjunction with a position sensor 53 that detects the position of the exposure target substrate 3 moving in relative fashion, and the pattern generator 52 thus generates the pattern data in a manner synchronized with the position of the exposure target substrate 3. A surface light source 2 projects light onto the DMD 51 through a diffusion plate 54 and a lens 55. The DMD 51 causes each of its tiny mirrors (micromirrors) to tilt according to the pattern data, thereby suitably changing the reflection direction of the light incident on each micromirror of the DMD 51; the resulting light is projected through a lens 56 onto the resist on the exposure target substrate 3 to form the exposure pattern corresponding to the pattern data.
In the direct exposure method, the light source for projecting the light onto the exposure target substrate must be constructed to provide uniform and evenly distributed light over the entire surface of the exposure target substrate in order to achieve a good exposure result.
FIG. 8 is a diagram showing one prior art example in which a surface light source comprising a plurality of point light sources is employed in order to provide uniform illumination in the direct exposure apparatus. The surface light source 2 is constructed by arranging the plurality of point light sources 58 in a two-dimensional array. The light from each point light source is first converged using an optical fiber and then converted by a convex lens into parallel light; then, the rays of parallel light are passed through the diffusion plate 54 to eliminate any “unevenness in illuminance,” and the thus produced light is projected onto the DMD 51 in FIG. 7.
In an alternative technique, light produced from a point light source is divided into a plurality of segments to achieve multiple light sources in an equivalent manner, and their light levels are equalized to achieve a surface light source.
Further, in Japanese Unexamined Patent Publication No. 2002-367900, there is disclosed a technique that provides uniform illumination over the entire surface of the exposure target substrate by controlling the tilt angle of each micromirror of the DMD based on data concerning the distribution of the amount of image light (the illuminance distribution) on the exposure target substrate.
Japanese Unexamined Patent Publication No. 2004-146789 also discloses a technique for providing uniform illumination over the entire surface of the exposure target substrate; according to this technique, the exposure is performed in the direction of scanning while displacing the exposure area in a direction orthogonal to the scanning direction in such a manner that the exposure area overlaps an exposure area adjacent to it.
When the surface light source is constructed by arranging a plurality of point light sources, if a method is employed that measures the illuminance distribution on the exposure surface of the exposure target substrate and that performs feedback control, using the measured results, to control the light-emission level of each individual point light source so that a uniform illuminance distribution is achieved over the entire exposure surface of the exposure target substrate, the amount of computation will become enormous, which is not desirable. Likewise, in the technique disclosed in Japanese Unexamined Patent Publication No. 2002-367900, the tilt angle of each micromirror is controlled so that a uniform illuminance distribution is achieved over the entire exposure surface of the exposure target substrate, but controlling the tilt angle of each individual micromirror by feedback control would not be desirable because it would require an enormous amount of computation. Such an increase in the amount of computation means that it takes a considerable time to determine the light-emission levels of all the point light sources that can achieve the uniform illuminance distribution.
In view of the above problem, it is an object of the present invention to provide a surface light source control apparatus and a surface light source control method for a direct exposure apparatus, wherein provisions are made to efficiently equalize the luminous intensity of a surface light source constructed from a plurality of point light sources.